Typical examples of allergic diseases include allergic rhinitis such as pollinosis, allergic conjunctivitis, atopic type bronchial asthma and atopic dermatitis, and in recent years, the morbidity rates of these allergic diseases in Japan just keep increasing. It is known that a significant number of the causes of onset for atopic type bronchial asthma or atopic dermatitis involve house dust, which includes mite bodies, mite feces, fungi, hairs of animals such as pets. Particularly, it is known that allergens derived from house dust mites inhabiting houses play an important role (Non-Patent Literature 1).
Most of typical house dust mites inhabiting houses consist of Dermatophagoides Farinae (hereinafter, abbreviated to “Der f ”) and Dermatophagoides pteronyssinus (hereinafter, abbreviated to “Der p”). These house dust mites are known to propagate most effectively under warm and humid conditions; however, in present times with an increased number of highly airtight and highly heat-insulated buildings, there are more chances that the indoor environment can be maintained under conditions adequate for house dust mites all year round, and thus the population of house dust mites is still increasing. This is believed to be a factor causative of the increase in allergic diseases.
For the treatment of these allergic diseases, for example, an antihistamine drug, a steroidal antiinflammatory drug, an antileukotriene drug, a degranulation inhibitor, and a Th2 cytokine inhibitor are used; however, all of these are merely for symptomatic treatments. Meanwhile, allergen immunotherapy including subcutaneous allergen immunotherapy (SLIT) and sublingual allergen immunotherapy (SLIT) have been successively developed in recent years. Allergen immunotherapy is a method of treatment by which immune responses to an allergen are controlled by administering the allergen to the body in small amounts, and at the present moment, it is considered that allergen immunotherapy is the only method capable of complete cure of allergic diseases.
Development of allergen immunotherapy must be accompanied by research and understanding of causative allergens. For example, highly antigenic allergens called Der f 1, Der f 2, and Der f 3 have been reported to be found in the body or feces of Dermatophagoides farinae, which is said to have a large population in Japan, and these allergens have already been cloned (Non-Patent Literatures 2 and 3). According to the past reports, it is known that 80% or more of patients suffering from mite allergy have IgE specific to anyone or more of these allergens (Non-Patent Literature 4). In addition, exploratory research for Dermatophagoides farinae allergens is being actively conducted, and thus there is a demand for novel allergen proteins that are more useful for the prevention and treatment of allergic diseases caused by mite (Non-Patent Literature 5).